At present, in a process for manufacturing a thin film transistor, an active layer is formed in such a manner: firstly, forming a semiconductor layer, and then, etching the semiconductor layer, so as to reserve the semiconductor layer in a channel region as the active layer.
Thus, the reserved semiconductor layer (i.e., the active layer) can be damaged by a process for etching the semiconductor layer, and even if an etch stop layer is formed on the semiconductor layer and damage brought to the reserved semiconductor layer by etching cannot be completely avoided.